FhirClient.CreateAsync返回null而非OperationOutcome问题排查

问题重现 #

已配置FhirClient创建AdverseEvent资源，代码如下：

var clientSettings = FhirClientSettings.CreateDefault();
clientSettings.PreferredReturn = Prefer.OperationOutcome;

var uri = $"https://psims-uat.azure-api.net/adverse-event/fhir";
var fhirClient = new FhirClient(uri, clientSettings, _handler);
return await fhirClient.CreateAsync<AdverseEvent>(adverseEvent);

当前代码返回null，但需要获取OperationOutcome提取警告信息，同时拿到已创建资源的ID。补充：_handler是用于添加订阅密钥的自定义HttpClientHandler，代码如下：

public class SubscriptionKeyHeaderHandler : HttpClientHandler 
{
    private readonly string subKey;
    private readonly string fhirVersion;

    public SubscriptionKeyHeaderHandler(string subKey, string fhirVersion ) : base()
    {
        this.subKey = subKey;
        this.fhirVersion = fhirVersion;
    }

    protected async override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        request.Headers.Add("Ocp-Apim-Subscription-Key", subKey);
        request.Headers.Add("Cache-Control", "no-cache");
        request.Headers.Add("fhir-version", fhirVersion);
        return await base.SendAsync(request, cancellationToken);
    }
}

问题原因 #

当设置clientSettings.PreferredReturn = Prefer.OperationOutcome时，Hl7.Fhir的FhirClient.CreateAsync<T>方法设计上不会返回创建的资源实例（因此返回null），但服务器返回的OperationOutcome和资源位置信息会被存储在FhirClient.LastResult属性中，而非直接作为返回值返回。

解决方案 #

修改代码，调用CreateAsync后通过fhirClient.LastResult获取所需信息：

var clientSettings = FhirClientSettings.CreateDefault();
clientSettings.PreferredReturn = Prefer.OperationOutcome;

var uri = $"https://psims-uat.azure-api.net/adverse-event/fhir";
var fhirClient = new FhirClient(uri, clientSettings, _handler);
// 调用CreateAsync，此时返回值为null，无需接收
await fhirClient.CreateAsync<AdverseEvent>(adverseEvent);

// 提取OperationOutcome
OperationOutcome operationOutcome = fhirClient.LastResult.OperationOutcome;

// 从Location头解析资源ID（Location格式通常为"{baseUrl}/AdverseEvent/{resourceId}"）
string resourceId = null;
var locationHeader = fhirClient.LastResult.Location;
if (!string.IsNullOrWhiteSpace(locationHeader))
{
    // 拆分路径获取ID，可根据实际返回格式调整逻辑
    var pathSegments = locationHeader.Split('/');
    resourceId = pathSegments.LastOrDefault();
}

// 提取警告信息（遍历OperationOutcome的Issue集合）
var warnings = operationOutcome?.Issue?.Where(i => i.Severity == IssueSeverity.Warning)
    .Select(i => i.Details?.Text)
    .ToList();

// 返回需要的信息，比如封装成自定义对象
return new 
{
    ResourceId = resourceId,
    OperationOutcome = operationOutcome,
    Warnings = warnings
};

额外检查点 #

• 确认FHIR服务器支持Prefer: operation-outcome请求头，部分服务器可能需要配置才能返回包含资源ID的OperationOutcome
• 验证SubscriptionKeyHeaderHandler添加的请求头是否符合服务器要求，确保请求能被正常处理
• 若LastResult.Location为空，可检查OperationOutcome的Issue中是否包含资源ID的相关描述

内容的提问来源于stack exchange，提问作者Mark Cooper